This application relates generally to communication systems, and, more particularly, to wireless communication systems.
Wireless communication systems use a network of access points such as base stations to provide wireless connectivity to various access terminals, such as mobile units and/or other devices that are enabled for wireless communication. The coverage area of a wireless communication system is typically divided into a number of geographic areas that are conventionally referred to as cells or sectors. The coverage area of each cell in the wireless network is limited by the propagation loss of radio signals transmitted by access points that provide coverage to the cell. Thus, the coverage area of each cell is determined by the location and the transmit power of the access point, as well as other factors including the geography of the cell and the location of any interfering objects. For example, the coverage area of a cell may be reduced if a building or a mountain is present near the access point. The boundaries of the cells are not rigidly defined and may vary with time. Thus, coverage areas may overlap such that multiple access points may provide coverage to the overlapping regions, although the strength of the signal provided within the overlapping regions may be different for the different access points.
Wireless communication standards such as Long Term Evolution (LTE, LTE-Advanced) support broadcasting or multicasting services such as the multimedia broadcast multicast service (MBMS) or the enhanced multimedia broadcast multicast service (eMBMS). The MBMS services broadcast or multicast data from base stations over the air interface on channels that can be received by one or more users. The eMBMS is an enhanced version that provides additional features such as an architecture and physical layer enhancements that allow the eMBMS service to carry multimedia information to user equipment. Typically, users subscribe to particular programs that they may then receive using the MBMS service. Once a user has subscribed to a program and begun to receive the program, the user expects to receive the program without interruption even though the user may move into or out of buildings, cars, buses and the like. However, any obstruction between the user and a base station can cause channel losses that reduce the signal strength of the MBMS signal. For example, building penetration losses are typically on the order of 11-20 dB and car penetration losses are typically on the order of 7 dB.